Assessing UAV Saturation Limits in Reserved Airspace for Safe Coexistence with Crewed Aircraft

The growing integration of UAS into airspace demands a comprehensive understanding of their safety implications, especially in scenarios involving low-flying non-cooperative drones and crewed aircraft. There is a critical need to estimate saturation points within Reserved Airspace environments, where an increase in UAV density can compromise safety metrics such as Well-Clear (WC) violations, Near Mid-Air Collisions (NMACs), and Mid-Air Collisions (MACs) for crewed aircraft (CAs), as well as small Near Mid-Air Collisions (sNMACs) and MACs for UAVs. These confined airspace refers to a designated portion of airspace reserved for specific purposes or activities, with restricted or controlled access to ensure safety and efficiency. In most cases, external UAVs and CAs may operate within an confined airspace if they are equipped with suitable Detect and Avoid (DAA) systems. This paper emphasizes the need to determine the saturation limit for the number of UAVs operating within a confined space and presents a method for its calculation. Simulations were conducted in a virtual environment replicating an agricultural field, where a crewed aircraft (crop duster) performs low-altitude operations. Two use cases were analyzed, both involving UAVs operating alongside the crewed aircraft sharing the same area, potentially leading to WC violations or even MACs. In both cases, the saturation point was identified by gradually increasing the number of UAVs operating in the field. The first use case involves linear inspections, where UAVs share a border of the shared operational area. This scenario is similar to power-line inspections or UTM corridors, where UAV navigation follows predictable and consistent paths. The simulation ensures that UAVs move to a safe area when a crewed aircraft is present and subsequently return to their original point to resume their trajectory. The second use case simulates a UAV package delivery operation, where UAV trajectories cross the CAs operational area. This scenario models unpredictable and inconsistent paths for UAVs as they traverse the field. In these scenarios, a simulated DAA system is employed, enabling drones to make autonomous decisions to avoid violating the WC range of the crewed aircraft while still completing their missions. The DAA system utilizes a heuristic approach, and the simulation assumes that UAVs are non-cooperative, meaning they cannot communicate or collaborate on positioning decisions. The primary objective of this paper is to identify the saturation point at which a UAV poses a risk to the crewed aircraft and other UAVs operating in the shared area. The proposed approach aims to assist regulators in determining the maximum number of UAVs that can safely operate within a area, given the UAV density, trajectory predictability, and DAA system performance. This work was conducted as part of the FAA/ASSURE-funded Right-of-Way Rules project.